1. Field of the Invention
The present invention relates to an optical pickup apparatus and an optical disk drive apparatus such as an optical card apparatus or so.
2. Description of the Related Art
FIG. 1 shows a general configuration of an optical pickup apparatus provided in an optical disk drive apparatus. As shown, the optical pickup apparatus handles an optical disk 8 and includes a semiconductor laser 1, a glass plate 2, a grating 3 formed on a side of the glass plate, which side faces the semiconductor laser 1, for generating three beams, a hologram 4 formed on a side of the glass plate, which side is opposite to the side on which the grating 3 is formed, a hologram pickup 5, a collimator lens 6, an objective lens 7, and a light receiving device 9.
FIG. 2 shows an internal side view of the hologram pickup 5. As shown, the hologram pickup 5 includes the semiconductor laser 1 and the light receiving device 9 mounted on a substrate, and also, the glass plate 2, grating 3 and hologram 4 arranged to face the semiconductor laser 1, and thus, these parts/devices form a unit.
A beam emitted from the semiconductor laser 1 is split into a main beam (0-th light) and two sub-beams (±1-st lights) by means of the grating 3 functioning as a diffraction grating for the three beams, and after that, reaches the hologram 4. Then, only a light (0-th light) transmitted by the hologram 4 is made to become a parallel beam by means of the collimator lens 6, and is collected onto the optical disk 8 after passing through the objective lens 7. Returning lights of the main beam and sub-beams reflected by the optical disk 8 are directed to the hologram 4 after again passing through the objective lens 7 and collimator lens 6. Then, at this time, only a light (1-st diffracted light) diffracted by the hologram 4 is applied to the light receiving device 9, and is used for generating various signals which will be described later.
The optical disk 8 includes two recording layers 8a and 8b with a separation of tens of μm (on the order of a range between 40 and 70 μm), and FIG. 1 shows a case where the beam applied is made to focus in the recording layer 8a nearer to the objective lens 7. Reflected light 10 indicated by a solid line in FIG. 1 is a beam which has been reflected by the recording layer 8a nearer to the objective lens 7, while reflected light 11 indicated by a broken line is a beam which was reflected by the recording layer 8b farther from the objective lens 7.
FIG. 3 illustrates a state of the reflected light 10 from the recording layer 8a and the reflected light 11 from the recording layer 8b in the hologram 4. As shown, the hologram 4 is separated into three areas AB, C and D defined by two separating lines.
FIG. 4 illustrates a state of the reflected light 10 from the recording layer 8a and the reflected light 11 from the recording layer 8b on the light receiving device 9. The total three beams, i.e., the main beam and two sub-beams provided by the grating 3 are split by the hologram 4. As a result, the reflected light 10 from the recording layer 8a forms nine spots while the reflected light 11 from the recording layer 8b forms nine flare without focusing.
As shown in FIG. 4, the light receiving device 9 includes eight light receiving surfaces ‘a’ through ‘h’, and relationship between beams obtained from the diffraction by the above-mentioned three areas AB, C and D of the hologram 4 and the light receiving surfaces receiving these beams respectively is as follows:
the diffracted light of the main beam from the area AB is received between the light receiving surfaces ‘a’ and ‘b’;
the diffracted lights of the sub-beams from the area AB are received outside of the light receiving surfaces ‘a’ and ‘b’, respectively (in other words, these are not substantially received by any of the light receiving surfaces);
the diffracted light of the main beam from the area C is received by the light receiving surface ‘c’;
the diffracted lights of the sub-beams from the area C are received by the light receiving surfaces ‘e’ and ‘g’, respectively;
the diffracted light of the main beam from the area D is received by the light receiving surface ‘d’; and
the diffracted light of the sub-beams from the area D are received by the light receiving surfaces ‘f’ and ‘h’ respectively.
By expressing the various signals obtained from the respective light receiving surfaces ‘a’ through ‘h’ by the respective same symbols ‘a’ through ‘h’, a focus error signal FES is expressed by:FES=a−b. A tracking error signal TES is expressed by:TES=(c−d)−α((e+g)−(f+h)).A tracking cross signal TCS is expressed by:TCS=(c+d)−α((e+g)+(f+h)).A lens position signal LPS is expressed by:LPS=(c−d)+α((e+g)−(f+h))An information reproducing signal RFS is expressed by:RFS=a+b+c+d. These relationships are obtained according to a so-called differential push-pull method well known.
Japanese patent No. 2594445 (registered in Dec. 19, 1996 and entitled ‘Hologram Optical Head’, the inventors: Shuichi Onayama et al.) and Japanese laid-open patent application No. H11-353698 (published in Dec. 24, 1999, entitled ‘Optical Pickup Apparatus’, the inventor: Masahiko Nakayama) disclose the background arts. Specifically, Japanese patent No. 2594445 discloses a hologram for a hologram optical head having a circular area at the center for making easier spot adjustment for returning light (see FIG. 1 of this patent). Japanese laid-open patent application No. H11-353698 discloses an optical pickup apparatus diffracting reflected light from an optical disk by means of a hologram so as to direct it toward a light receiving device (see FIG. 1 of this laid-open patent application)
FIG. 5 shows a general configuration of another optical pickup apparatus in an optical disk drive apparatus. As shown, the optical pickup apparatus handles an optical disk 108 and includes a semiconductor laser 101, a glass plate 102, a grating 103 formed on a side of the glass plate, which side faces the semiconductor laser 101, for generating three beams, a hologram 104 formed on a side of the glass plate, which side is opposite to the side on which the grating 103 is formed, a hologram pickup 105, a collimator lens 106, an objective lens 107, and a light receiving device 109.
FIG. 6 shows an internal side view of the hologram pickup 105. As shown, the hologram pickup 105 includes the semiconductor laser 101 and the light receiving device 109 mounted on a substrate, and also, the glass plate 102, grating 103 and hologram 104 arranged to face the semiconductor laser 101, and thus, these parts/devices form a unit.
A beam emitted from the semiconductor laser 101 is split into a main beam (0-th light) and two sub-beams (±1-st lights) by means of the grating 103 functioning as a diffraction grating for the three beams, and after that, reaches the hologram 104. Then, only a light (0-th light) transmitted by the hologram 104 is made to become a parallel beam by means of the collimator lens 106, and is collected onto the optical disk 108 after passing through the objective lens 107. Returning lights of the main beam and sub-beams reflected by the optical disk 108 are directed to the hologram 104 after again passing through the objective lens 107 and collimator lens 106. Then, at this time, only a light (1-st diffracted light) diffracted by the hologram 104 is applied to the light receiving device 109, and is used for generating various signals.
FIG. 7 illustrates a state of the reflected light 110 from the optical disk 108, on the hologram 104. As shown, the hologram 104 is separated into three areas AB, C and D by two separating lines. In FIG. 7, zones hatched denote zones at which a push-pull component occurs. Details of the push-pull signal are disclosed by Japanese patent publication No. H04-3013 (published on Jan. 21, 1992, entitled ‘Optical Track Position Detection Apparatus and Optical Recording/reproduction Apparatus applying it’, inventors: Shigeru Nakamura et al.)
Specifically, Japanese patent publication No. H04-3013 discloses an optical detector for detecting tracking error provided in a form symmetrical with respect to the track direction and disposed in a region within an interference region of 0-th diffracted light and ±1 diffracted light and further narrowed for the amount of maximum moving range of optical axis error of the reflected light caused in a tracking process or by disk inclination (see FIG. 9 of this publication).
FIG. 8 illustrates a state of the reflected light 110 from the optical disk 108, on the light receiving device 109. As shown, the light receiving device 109 includes eight light receiving surfaces ‘a’ through ‘h’, and relationship between beams obtained from the diffraction by the above-mentioned three areas AB, C and D of the hologram 4 and the light receiving surfaces receiving these beams respectively is as follows:
the diffracted light of the main beam from the area AB is received between the light receiving surfaces ‘a’ and ‘b’;
the diffracted lights of the sub-beams from the area AB are received outside of the light receiving surfaces ‘a’ and ‘b’, respectively (in other words, are not substantially received by any light receiving surfaces);
the diffracted light of the main beam from the area C is received by the light receiving surface ‘c’;
the diffracted lights of the sub-beams from the area C are received by the light receiving surfaces ‘e’ and ‘g’, respectively;
the diffracted light of the main beam from the area D is received by the light receiving surface ‘d’; and
the diffracted lights of the sub-beams from the area D are received by the light receiving surfaces ‘f’ and ‘h’ respectively.
By expressing the various signals obtained from the respective light receiving surfaces ‘a’ through ‘h’ by the same symbols ‘a’ through ‘h’ respectively, a focus error signal FES is expressed by:FES=a−b. A tracking error signal TES is expressed by:TES=(c−d)−α((e+g)−(f+h)).A tracking cross signal TCS is expressed by:TCS=(c+d)−α((e+g)+(f+h))A lens position signal LPS is expressed by:LPS=(c−d)+α((e+g)−(f+h))An information reproducing signal RFS is expressed by:RFS=a+b+c+d. 
In the push-pull signal (PPS) obtained from the hatched zones shown in FIG. 7, the rate at which this signal is included in the areas C and D is 50% of the whole signal amount as shown. This signal amount is sufficient in case where information such as addresses or so is detected from a pre-groove of a CD-R/RW.
Other than the above-mentioned Japanese laid-open patent publication No. H04-3013, Japanese laid-open patent application No. H11-353698 (mentioned above) also discloses the background art.